1. Technical Field of the Invention
The present invention generally relates to Resilient Packet Ring (“RPR”) networks. More particularly, and not by way of any limitation, the present invention is directed to system and method for reacting to miscabling defects in such networks.
2. Description of Related Art
FIG. 1 illustrates a block diagram of an RPR network 100 comprising four nodes A, B, C, and D, connected in a ring. Each node A-D is connected to adjacent nodes by at least one link in each of a clockwise and a counter-clockwise direction. In particular, in FIG. 1, links 102a-102d comprise a clockwise ring and links 104a-104d comprise a counter-clockwise ring. It will be assumed for the sake of example that the RPR protocol employed herein is the one currently being standardized as IEEE 802.17.
Miscabling is a failure condition in which packets sent by a node (e.g., node A) on one ring, such as the clockwise ring, are received on the other ring, i.e., the counter clockwise ring. Miscabling defects can eventually be remedied only manually by the operator; however, the method by which adjacent nodes react to a miscabled link affects the operation of the adjacent nodes and, in turn, the operation of the entire RPR network 100. The current IEEE 802.17 standard treats a miscabling defect as a fault condition referred to as a “Signal Fail” or “SF”. This situation results in unexpected, unintended, and undesirable consequences, as will be described in detail below.
Each of FIGS. 2A-2C depicts a different miscabling situation in the RPR 100 that may occur in connection with node A. In particular, in FIG. 2A, the receiving links of node A, specifically, link 200 and link 202, are miscabled, such that node A receives packets from node B on the counterclockwise ring, rather than on the clockwise ring as expected, and receives packets from node C on the clockwise ring, rather than on the counterclockwise ring as expected. In this situation, node A will detect miscabling defects on both links 200, 202, based on topology protection (“TP”) frames received from nodes B and C.
FIG. 2B illustrates a situation in which the sending links of node A, specifically, link 204 and link 206, are miscabled, such that packets from node A are received by node B on the clockwise ring, rather than on the counterclockwise ring as expected, and packets from node A are received by node C on the counterclockwise ring, rather than on the clockwise ring as expected. In this situation, node B will detect a miscabling defect on the link 204 based on TP frames received from node A. Similarly, node C will detect a miscabling defect on the link 206 based on TP frames received from node A.
FIG. 2C illustrates a situation in which both the sending and receiving links of node A, specifically, links 200-206, are miscabled. In this situation, node A will detect miscabling defects on both links 200 and 202, based on TP frames received from nodes B and C, node B will detect a miscabling defect on the link 204 based on TP frames received from node A, and node C will detect a miscabling defect on the link 206 based on TP frames received from node A.
Currently, the solution for all three types of miscabling defects illustrated in FIGS. 2A-2C is to isolate node A, enable edge status on both sides of node A, on the side of node B that, absent a miscabling defect, interfaces with node A, and on the side of node C that, absent a miscabling defect, interfaces with node A. This technique is illustrated in FIG. 3. The IEEE 802.17 standard implementation assumes that only adjacent nodes can detect miscabling defects.
Referring to FIG. 2B, in the current implementation of the IEEE 802.17 standard, in response to the illustrated miscabling condition, at node B or C, a TP frame is received from node A and forwarded to a Protection State Machine (“PSM”) within node B or C. The PSM within node B or C runs as if there were no miscabling defect. This is because in the current IEEE 802.17 standard implementation, detection of miscabling is not performed inside the PSM, but within a Topology Database State Machine (“TDSM”). After the PSM, the TDSM runs. As previously indicated, the miscabling defect will be detected within the TDSM and a flag is set to true.
The standard does not indicate what entity is to read this flag or when it will be read. Moreover, the standard states that the node detecting the miscabling defect should go into Signal Fail (“SF”) state and remain there until the miscabling is cleared.
As previously indicated, miscabling is not treated as a separate condition inside the PSM and is lumped together with the SF condition. This results in unintended consequences. Miscabling may be overwritten by other failure conditions at nodes B or C, such as SF status, or by conditions elsewhere in the network. As a result, in the prior art, new information from the hardware indicating a Signal Degrade (“SD”) condition on the link will simply overwrite the SF status because the SD condition comprises newer information about the situation on the link. Moreover, because SD conditions have lower priority than SF conditions, the original miscabling information on nodes B and C will be lost. This is an undesirable result. Furthermore, an SD on a first link may be preempted by a worse condition on another link, such as SF, elsewhere in the network 100 according to the IEEE 802.17 standard implementation. In this situation, the miscabled link enters the IDLE state and hence becomes fully operational. Again, in this situation, the error due to the miscabling defect is lost.
If miscabling is treated as an SF condition, then an SD condition received from the hardware is lost. In particular, if new hardware conditions are ignored and the node remains in an SF condition, information received from hardware indicating an SD condition is lost. After clearance of the miscabling defect, the link returns to IDLE instead of SD. This is clearly not a desirable result.